Now that I have these 2 (Block Letter and Signature), I'm going to open both and demythify if there is any difference or not between them.
I always heard lots of stories about different transformers, different capacitors, different circuit, etc.
I'll take some pics of the differences (if they exist) and post them here.

This one cost me around 700Eur inc. shipping, but it is in original condition and very well treated.
I haven't seen much of these in this condition on Ebay.
It doesn't look like an amp that is 17 years old.